Thrombosis and Embolism. 351 



Causes of Thrombus. The production of a thrombus maj' be 

 due to the condition of the blood or of the vessels. The researches 

 of Buchanan, Schmidt, Hammersten and others show that two 

 albuminoid elements, fibrinogen and paraglobulin, present in the 

 living blood, and a fibrine ferment mainly derived from the white 

 corpuscles iti process of change or destruction, determine power- 

 fully the formation of fibrine and clot. Hewson, Briicke and Lis- 

 ter have shown that blood may be maintained fluid for many 

 hours in an unimpaired vein, or turtle's heart thoguh it may have 

 been removed from the body, the important condition being that 

 the vein shall retain its vitality and suffer no derangement of its 

 endothelium. I,ister has even shown that blood may remain 

 fluid for many hours in a sterilized glass tube which has been 

 filled by passing the tube carefully in'to such a vein without dis- 

 turbing its lining membrane, or imparting motion to the liquid. In 

 such a case a thin film of coagulum only, forms on the interior of the 

 glass tube. In healthy blood, without addition of any extraneous 

 matter, and kept perfectly still, the plasma and globules retain 

 their integrity, and the former its fluidity for a length of time. 

 But if shed into a basin it coagulates at once. 



a. Changes in the blood. Contact with foreign bodies generally 

 deterraines-this change and prompt coagulation. Transfixing the 

 artery with a needle, even a silver one, the entrance of parasites 

 (actinomycosis, strongyli, filaria), the presence of pus, and of 

 certain infectious microbes and their products, the introduction of 

 solid particles f.nd even of air into the vessels, the transfusion of 

 blood which has been exposed to receive aerial germs, or which 

 contains microscopic clots, or the globules of which have become 

 modified by contact with a basin or other vessel, even the trans- 

 fusion of defibrinated blood may cause coagulation. The danger 

 is always greater if the blood is drawn from a different genus and 

 unfitted to live in the blood of the recipient. Disease germs are 

 especially dangerous if adapted to colonize the serosa of the ves- 

 sel and destroy its epithelium. A decrease of the density of the 

 blood favors coagulation, a lowering of one thousandth rendering 

 it syrupy, and various chemical agents induce or favor coagulation, 

 thus acetic acid, valerianic acid, alcohol, the salts of iron, and 

 above all the salts of lime act in this way. Very high and low 

 temperatures throw down the fibrine as a grumous precipitate, but 

 the clot remains soft. 



